The invention concerns a lubricant for metal strip, in particular for blank and painted strips made of aluminum or aluminum alloys and used for packaging, in particular for the packaging of foodstuffs.
Containers which can be used in the packaging of foodstuffs and the like, can be produced in a conventional manner by deep drawing material such as aluminum strip which is generally blank or painted before this operation. In order that the strip can be readily processed in various subsequent operations, the surface of the strip must exhibit good slip properties. Depositing a lubricant on the surface of the strip in one of the production steps (after painting, for instance) produces the desired effects. The surfaces bearing a lubricant must meet the following requirements:
(a) The ease of slip between two surfaces with a lubricant on them must be as great as possible.
(b) Easy slip must be maintained for a long time, more than two years, for instance. The substance providing easy slip must be able to withstand air, oxygen and light under normal storage conditions and must not lose its lubricating properties.
(c) The lubricating effect of the slip promoting agent must be so good that the material bearing the lubricant can be used, without any additional lubricant, for the production of containers by deep drawing.
(d) The lubricant must not give off any smell. In particular, the blank or painted thin strip product bearing the lubricant must not give off any smell when heated. In other words, the lubricant must exhibit thermal stability.
(e) The coating of lubricant must prevent the contents from sticking to the sheet, even after relatively strong heating, such as in baking.
(f) The coating of lubricant on baked lacquer coated strip may alter the thermal sealing characteristics only to a controllable degree.
(g) The lubricant must not react with lacquer coatings and must not cause swelling or dissolution of lacquer coatings. The components making up the lubricant must be in full accordance with the laws concerning foodstuffs.
The fluid substances used as lubricants up to now, such as paraffin oil and synthetic triglyceride, fulfill the above requirements only in part.
Furthermore, in some countries efforts are being made which would to a large degree prevent paraffin oil from being used as a lubricant on containers for foodstuffs.